The oldest fossil life on Earth consists of stromatolites, which are the remains of complicated communities of bacteria captured in rock. On modern Earth, similar communities still grow in places that are too harsh for worms, snails, and other grazing animals to live and eat them. Lakes in Antarctica with liquid water below a few meters of ice almost always support these communities. Thus, they provide the opportunity to study the ecology of microbial communities like those on early Earth billions of years ago